The effect of light on the gibberellin metabolism and growth of Phaseolus coccineus seedlings.

Light inhibits the rate of stem elongation of Phaseolus coccineus L. seedlings. Gibberellin A4 (GA4), an endogenous component of Phaseolus seedlings (Bowen et al., Phytochem. 12, 2935-2941, 1973) promotes stem growth in the light but not in darkness. Dark-grown seedlings contain larger GA pools than light-grown plants. Apically applied [(3)H]GA4 in etiolated bolised more extensively in the light. The slower rate of metabolism of [(3)H]GA4 in etiolated seedlings is not a consequence of isotopic dilution by the endogenous GA4 pool or a lack of penetration of the labelled material. While it can be concluded that the capacity of seedlings to metabolise [(3)H]GA4 is greater in the light than in darkness, it does not necessarily follow that there is a more rapid rate of turnover of endogenous GA4 in light-grown tissues. The results are discussed in relation to the involvement of GAs in the inhibitory effects of ligh on stem elongation.